Magnetic compensator



July 28, 1936. c. H. coLvlN MAGNETIC COMPENSATOR Filed Sept. 18, 1934ccc: n

VWM/TOR m u. 11W

Patented July 28, 1936 PATENT OFFIE MAGNETIC COMPENSATOR Charles H.Colvin, Morris Township, Morris County, N. J.

Application September 18, 1934, Serial No. '144,491

3 Claims.

This invention relates to improvements in compensators for magneticCompasses and to the method of their use.

Magnetic compensators have been of three general types: first, thoseemploying removable magnets (of various sizes or strengths) in fixedpositions; second, those employing non-removable magnets of which theeffective magnetic characteristics are variable; and third, thoseemploying removable magnets in variable positions.

Compensators of the first type have had the advantage of simplicity, butthe disadvantage of relative inaccuracy and awkwardness of use. Those ofthe second type have been compact, easily adjusted, and relativelyaccurate in the correction of semi-circular errors. They have had thedisavantage of not only providing no correction for heeling errors butof actually introducing or intensifying such errors. Those of the thirdtype have had the advantages of accuracy and ease of adjustment, buthave been too complicated and bulky to be useful upon aircraft,automobiles or small boats.

This invention relates more particularly to improvements in compensatorsof this third type.

It is an object of this invention to provide a compensator which issimple, rugged, compact, accurate in the correction of bothsemi-circular and heel errors, and easy to manipulate.

Other objects and advantages will appear as the invention is disclosedand described.

Without limiting myself to the particular forms illustrated, I showpreferred embodiments of the invention in the accompanying drawing, asfollows:

Figure 1 is a vertical section through the compensator (on the line I-Iof Figure 3) in a form adapted for use with an aircraft compass, towhich the compensator is shown attached.

Figure 2 is an elevation view of the compensator, partly in section (onthe line 2-2 of Figure 3).

Figure 3 is a horizontal section through the compensator on the lines3-3 of Figures 1 and 2.

Figure 4 shows, in section, an alternate form of heeling corrector.

Figure 5 is a chart to which reference will be made in explaining themethod of using the compensator on a boat or airplane.

Referring now more particularly to the drawing, the compass I Irepresented in Figure 1 forms no part of this invention and is shown toillustrate the mounting of the compensator in relation to the magnets I2of the magnetic element I3 of the compass. The mounting plate or closuremember I4 of the compensator is attached by-screws Iii-to the bottom ofthe bowl I1 of the compass I I. It will be appreciated that differenttypes of compass will necessitate different methods of attachment of thecompensator, and that 5 it is not necessary that the compensator beattached directly to the compass, as each may be independently attachedto a part of the aircraft or boat.

Journaled in the plate I4 is a support or jack- 10 screw I8 to which isattached bottom plate or closure member I9 by nut 2I, in such a way thatplate I9 is fast to screw I8 and both parts are movable together as aunit. Plate I9 has a knurled rim 22 by which it may be turned.

Interposed between plates I4 and I9, and journaled upon both plates, isan outer case or housing 23 which has near its upper edge a knurled rim24 by which it may be turned. Above this rim, and readable against anindex 26 on plate I4, is 2O a circular scale 21, graduated in degrees orotherwise, in a direction which is the reverse of the normal compassrose; i. e., the graduations proceed from 0 to 360 in a counterclockwisedirection when viewed from above.-

Within the housing 23 are two bosses 28 and 29 through which extendholes parallel to the axis of jack-screw I8. Matching with the ends ofthese holes are a series of depressions on the under surface of plate I4and on the upper surface 30 of plate I9. Within one of these holes aretwo detent plungers 3| and 32, pressed apart by a spring 33. Theseplungers, with the corresponding depressions in plates I4 and I9, tendto hold plate I9 in relation to barrel 23, and to hold bar- 35 rel 23 inrelation to plate I4.

Within the other of these holes are two additional detent plungers 34and 36. These are controlled by the positions of lock-screws 31 and 38,the upper of which is shown in the unlocked posi- 40 tion, releasingplunger 34 from locking contact with a depression in plate I4, and thelower of which is shown in the locked position, holding plunger 36 inlocked relation with plate I9. Holes 39 and 4I are provided in screws 31and 38 through 45 which a safety or sealing wire may be secured.

Jack-screw I8 carries a thread, preferably a multiple thread, on itssurface, on which rides a follower-nut 42 to which are secured magnettubes or casings 43 and 44. These tubes encase mag- 50 nets 46 and 41,which are removable when desired through holes 48 and 49 in barrel 23.

Tubes 43 and 44 are guided against rotation by sliding on the sides ofbosses 28 and 29.

It is thus apparent that rotation of housing 23 55 in reference to plateI4 rotates or orients magnets 46 and 4l, through an angle which may beread on scale 2l, and that rotation of plate I9 in reference to housing23 raises or lowers magnets 46 and 41, thus decreasing or increasingtheir distance from the magnets I2 of the compass II.

Axially slidable within screw I8 is a tube 48 which contains a verticalmagnet 49. The position of tube 48 may be manually adjusted and lockedVby a clutch consisting of jaws 5I on screw I8, which are closedby a nut52, or as shown in Figure 4, tube 48 may be threaded and have aprojecting key 53, being raised and lowered by the" rotation of nut 54.v

The method of using this invention upon aircraft, boats and automobileswill now be described. If an airplane or boat be headed successively invarious directions, the readings of its compass (without correction)noted, and the errors plotted against true magnetic directions, a graphsimilar to the solid line or Figure v5 will be obtained. Here theVerrors in readings higher than true have been plotted above thereference line and minus errors plotted below the line. As is apparentfrom the Vcurve there aretwo positions (at N and S) where no correctionis needed, and two positions (near E and W) where maximum correction isneeded. AOn the craft which gave the curve shown it is apparent that thelocal magnetism, which the compensator is to balance out, lies inafore-and-aft direction, since there is no error in the compassindication when the craft is headed north or south. That is to say, whenthe craft is headed north or south thereis no error, and hence thedirection of the earths magnetism and the direction of the localmagnetism must coincide. VThe compensating magnetsare now inserted inthe tubes 43 and 44 through the holes 48 and 49, in such a way thattheir north-.seeking ends are under the letter S of the scale 2'I. (Theycould of course be inserted with their north-seeking ends under theletter N, in which case the following description must be transferred180.) Weaker or stronger magnets will be inserted, ac'- cording to themagnitude of the errors to be corrected. The barrel Y23 is then turnedin reference to the plate I4 until theN (or zero) comes in line with theindex 2,6. I

The airplane-or boat is now headed inthek direction of maximum error, orin a direction about from that of minimum or zero error, and the lowerplate I9 is turned, raising the magnets, until the compass readscorrectly, that is until the error is reduced to zero or a minimum-.-

The craft is now swung again, noting the compass readings which whenplotted as error may give a curve as shown in dash line in Figure 5.

Heeling correction is next made.v If the air;

plane, which was assumed to be in itsv normal flying attitude during thepreceding` swinging,

now has its Atail wheel lowered to the ground (or in the case of a boatif ballast is shifted to produce a heavy list) and is again swung,compass readings if plotted as errors would give a curve like the dottedline of Figure 5. It is not necessary to make such a curve, however, butmerely to determine a direction in which there is a large heeling error.With the craft in this position the tube 48 is inserted with a magnetinside, and raised until the compass indicates correctly, at which timeit is locked in position (or if the structure of Figure 4 is being used,simply left in position). If the craft is now swung and the compasserrors plotted the curve should be that shown in small circles.

tical, hollow, threaded support rotatably carried by said plate, acasing carried upon said support for threaded adjustment therealong, amagnet carried in said casing, a baseplate fixed to and carried by said'supportya cylindrical member carried between said two plates whereby toform a chamber enclosing said magnet and casing, guide members carriedby and within said cylindrical member and engaging with` said casing formaintaining xed the angular. relation of said casing and magnetrelatively to said cylindricalmember, said cylindrical member and casingVbeing orientable 'relatively to said mounting plate and bearingcooperating yindicia indicating their relative angular position, saidsupport and base plate being rotatable relatively to said cylindricalmember to cause ax'ial motion of said casing and magnetfrelatively tosaid cylindrical member and. support, .a second casing vwithin' saidsupport, said. second casing carrying a second magnetfihianormallyvertical position `and'being' axially adjustable within said support.

, 2. A compensator in accordance with claim -1-,- with detentmeansbetween said cylindrical meinber and said mounting plate, detentmeans between said base plate and said cylindrical meinber,'lockingmeansbetween said cylindrical ineinber and saidmounting plate, and lockingmeans. between said base .plate and said cylindrical member.k l v V3. Acompensator for a magnetic compass, coinprising in combination, acasing, a r'nagnet car'- ried inisaidcasing', a support' for said'casing-,v a hollow cylindrical housing, said casing arid said supportbeing carried within said housing, substantially flat top and bottom'closure members for'said housing, said support being rotatable in saidtop closure member and xed to said bottom closure member, said housingbeing rotatable in respect to said top member to effect orientation ofsaid magnet and casing', and said bottom (member and said support beingrotatable in respect to said `housing to effect movement of saidY magnetand casing along the' aX'is of rotation of said support. 1

